Radio communications involving at least one vehicle, also referred to as vehicle-to-everything (V2X) communications, carry both non-safety and safety information. Hence, applications and services using the V2X communications are associated with a specific set of requirements, e.g., in terms of latency, reliability, capacity, etc. for transmitting messages known as Common Awareness Messages (CAM) and Decentralized Notification Messages (DENM) or Basic Safety Message (BSM). The data volume of these messages is very low compared to mobile broadband (MBB) communications. Rather, safety-related V2X communications usually require high reliability, low latency and instant communication.
At least in certain situations, these requirements can be fulfilled only if the transmission is self-contained, that is by including control information and data in one transmission time interval (TTI). By blindly decoding the control information scrambled with an identifier, the identified radio device can receive the control information, e.g., a scheduling assignment, for instant data reception.
Moreover, to realize sufficient link margin or allow frequency reuse, transmitter and/or receiver use large antenna arrays for directional beamforming. However, each antenna port of the antenna arrays at transmitter and receiver has to be coupled to a radio chain for precoding and channel estimation, respectively, in the digital domain. To reduce the costs and power consumption of such radio chains, precoding and channel estimation can be divided between the analog domain and the digital domain. A. Alkhateeb et al. describe in the document “Channel Estimation and Hybrid Precoding for Millimeter Wave Cellular Systems”, IEEE J. Sel. Topics Signal Process., vol. 8, no. 5, October 2014, pp. 831-46, such a radio device including both an analog radio frequency beamformer and a digital baseband beamformer.
However, at the time of a self-contained transmission, the radio device supposed to receive the self-contained transmission has no knowledge as to the state of the radio channel between transmitter and receiver. Hence, the radio frequency beamformer at the receiver has to sweep its directional gain until reference signals are received from the transmitter for channel estimation and subsequent reception of the control information and the data. Such an unpredictable delay is unacceptable for many radio applications, particularly in V2X communications.